/
rgb_to_256.go
376 lines (359 loc) · 7.08 KB
/
rgb_to_256.go
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package color
import (
"fmt"
"math"
)
// adapted from https://gist.github.com/MicahElliott/719710
var (
c256ToRgb = map[uint8]string{}
// rgb to 256 color look-up table
lookupTable = map[string]uint8{
// 8-bit, RGB hex
// Primary 3-bit (8 colors). Unique representation!
"000000": 0,
"800000": 1,
"008000": 2,
"808000": 3,
"000080": 4,
"800080": 5,
"008080": 6,
"c0c0c0": 7,
// Equivalent "bright" versions of original 8 colors.
"808080": 8,
"ff0000": 9,
"00ff00": 10,
"ffff00": 11,
"0000ff": 12,
"ff00ff": 13,
"00ffff": 14,
"ffffff": 15,
// values commented out below are duplicates from the prior sections
// Strictly ascending.
// "000000": 16,
"000001": 16, // up: avoid key conflicts, value + 1
"00005f": 17,
"000087": 18,
"0000af": 19,
"0000d7": 20,
// "0000ff": 21,
"0000fe": 21, // up: avoid key conflicts, value - 1
"005f00": 22,
"005f5f": 23,
"005f87": 24,
"005faf": 25,
"005fd7": 26,
"005fff": 27,
"008700": 28,
"00875f": 29,
"008787": 30,
"0087af": 31,
"0087d7": 32,
"0087ff": 33,
"00af00": 34,
"00af5f": 35,
"00af87": 36,
"00afaf": 37,
"00afd7": 38,
"00afff": 39,
"00d700": 40,
"00d75f": 41,
"00d787": 42,
"00d7af": 43,
"00d7d7": 44,
"00d7ff": 45,
// "00ff00": 46,
"00ff01": 46, // up: avoid key conflicts, value + 1
"00ff5f": 47,
"00ff87": 48,
"00ffaf": 49,
"00ffd7": 50,
// "00ffff": 51,
"00fffe": 51, // up: avoid key conflicts, value - 1
"5f0000": 52,
"5f005f": 53,
"5f0087": 54,
"5f00af": 55,
"5f00d7": 56,
"5f00ff": 57,
"5f5f00": 58,
"5f5f5f": 59,
"5f5f87": 60,
"5f5faf": 61,
"5f5fd7": 62,
"5f5fff": 63,
"5f8700": 64,
"5f875f": 65,
"5f8787": 66,
"5f87af": 67,
"5f87d7": 68,
"5f87ff": 69,
"5faf00": 70,
"5faf5f": 71,
"5faf87": 72,
"5fafaf": 73,
"5fafd7": 74,
"5fafff": 75,
"5fd700": 76,
"5fd75f": 77,
"5fd787": 78,
"5fd7af": 79,
"5fd7d7": 80,
"5fd7ff": 81,
"5fff00": 82,
"5fff5f": 83,
"5fff87": 84,
"5fffaf": 85,
"5fffd7": 86,
"5fffff": 87,
"870000": 88,
"87005f": 89,
"870087": 90,
"8700af": 91,
"8700d7": 92,
"8700ff": 93,
"875f00": 94,
"875f5f": 95,
"875f87": 96,
"875faf": 97,
"875fd7": 98,
"875fff": 99,
"878700": 100,
"87875f": 101,
"878787": 102,
"8787af": 103,
"8787d7": 104,
"8787ff": 105,
"87af00": 106,
"87af5f": 107,
"87af87": 108,
"87afaf": 109,
"87afd7": 110,
"87afff": 111,
"87d700": 112,
"87d75f": 113,
"87d787": 114,
"87d7af": 115,
"87d7d7": 116,
"87d7ff": 117,
"87ff00": 118,
"87ff5f": 119,
"87ff87": 120,
"87ffaf": 121,
"87ffd7": 122,
"87ffff": 123,
"af0000": 124,
"af005f": 125,
"af0087": 126,
"af00af": 127,
"af00d7": 128,
"af00ff": 129,
"af5f00": 130,
"af5f5f": 131,
"af5f87": 132,
"af5faf": 133,
"af5fd7": 134,
"af5fff": 135,
"af8700": 136,
"af875f": 137,
"af8787": 138,
"af87af": 139,
"af87d7": 140,
"af87ff": 141,
"afaf00": 142,
"afaf5f": 143,
"afaf87": 144,
"afafaf": 145,
"afafd7": 146,
"afafff": 147,
"afd700": 148,
"afd75f": 149,
"afd787": 150,
"afd7af": 151,
"afd7d7": 152,
"afd7ff": 153,
"afff00": 154,
"afff5f": 155,
"afff87": 156,
"afffaf": 157,
"afffd7": 158,
"afffff": 159,
"d70000": 160,
"d7005f": 161,
"d70087": 162,
"d700af": 163,
"d700d7": 164,
"d700ff": 165,
"d75f00": 166,
"d75f5f": 167,
"d75f87": 168,
"d75faf": 169,
"d75fd7": 170,
"d75fff": 171,
"d78700": 172,
"d7875f": 173,
"d78787": 174,
"d787af": 175,
"d787d7": 176,
"d787ff": 177,
"d7af00": 178,
"d7af5f": 179,
"d7af87": 180,
"d7afaf": 181,
"d7afd7": 182,
"d7afff": 183,
"d7d700": 184,
"d7d75f": 185,
"d7d787": 186,
"d7d7af": 187,
"d7d7d7": 188,
"d7d7ff": 189,
"d7ff00": 190,
"d7ff5f": 191,
"d7ff87": 192,
"d7ffaf": 193,
"d7ffd7": 194,
"d7ffff": 195,
// "ff0000": 196,
"ff0001": 196, // up: avoid key conflicts, value + 1
"ff005f": 197,
"ff0087": 198,
"ff00af": 199,
"ff00d7": 200,
// "ff00ff": 201,
"ff00fe": 201, // up: avoid key conflicts, value - 1
"ff5f00": 202,
"ff5f5f": 203,
"ff5f87": 204,
"ff5faf": 205,
"ff5fd7": 206,
"ff5fff": 207,
"ff8700": 208,
"ff875f": 209,
"ff8787": 210,
"ff87af": 211,
"ff87d7": 212,
"ff87ff": 213,
"ffaf00": 214,
"ffaf5f": 215,
"ffaf87": 216,
"ffafaf": 217,
"ffafd7": 218,
"ffafff": 219,
"ffd700": 220,
"ffd75f": 221,
"ffd787": 222,
"ffd7af": 223,
"ffd7d7": 224,
"ffd7ff": 225,
// "ffff00": 226,
"ffff01": 226, // up: avoid key conflicts, value + 1
"ffff5f": 227,
"ffff87": 228,
"ffffaf": 229,
"ffffd7": 230,
// "ffffff": 231,
"fffffe": 231, // up: avoid key conflicts, value - 1
// Gray-scale range.
"080808": 232,
"121212": 233,
"1c1c1c": 234,
"262626": 235,
"303030": 236,
"3a3a3a": 237,
"444444": 238,
"4e4e4e": 239,
"585858": 240,
"626262": 241,
"6c6c6c": 242,
"767676": 243,
// "808080": 244,
"808081": 244, // up: avoid key conflicts, value + 1
"8a8a8a": 245,
"949494": 246,
"9e9e9e": 247,
"a8a8a8": 248,
"b2b2b2": 249,
"bcbcbc": 250,
"c6c6c6": 251,
"d0d0d0": 252,
"dadada": 253,
"e4e4e4": 254,
"eeeeee": 255,
}
incs = []uint8{0x00, 0x5f, 0x87, 0xaf, 0xd7, 0xff}
)
// RgbTo256Table mapping data
func RgbTo256Table() map[string]uint8 {
return lookupTable
}
// Rgb2short convert RGB-code to 256-code
func Rgb2short(r, g, b uint8) uint8 {
res := make([]uint8, 3)
for partI, part := range [3]uint8{r, g, b} {
i := 0
for i < len(incs)-1 {
s, b := incs[i], incs[i+1] // smaller, bigger
if s <= part && part <= b {
s1 := math.Abs(float64(s) - float64(part))
b1 := math.Abs(float64(b) - float64(part))
var closest uint8
if s1 < b1 {
closest = s
} else {
closest = b
}
res[partI] = closest
break
}
i++
}
}
hex := fmt.Sprintf("%02x%02x%02x", res[0], res[1], res[2])
equiv := lookupTable[hex]
return equiv
}
// C256ToRgb convert an 256 color code to RGB numbers
func C256ToRgb(val uint8) (rgb []uint8) {
// TODO use sync.Once
if len(c256ToRgb) == 0 {
for hex, c256 := range lookupTable {
c256ToRgb[c256] = hex
}
}
hex, ok := c256ToRgb[val]
if false == ok {
return
}
// convert to rgb code
rgbInts := Hex2rgb(hex)
return []uint8{
uint8(rgbInts[0]),
uint8(rgbInts[1]),
uint8(rgbInts[2]),
}
}
// C256ToRgbV1 convert an 256 color code to RGB numbers
// refer https://github.com/torvalds/linux/commit/cec5b2a97a11ade56a701e83044d0a2a984c67b4
func C256ToRgbV1(val uint8) (rgb []uint8) {
var r, g, b uint8
if val < 8 { // Standard colours.
// r = val&1 ? 0xaa : 0x00;
r = compareVal(val&1 == 1, 0xaa, 0x00)
g = compareVal(val&2 == 2, 0xaa, 0x00)
b = compareVal(val&4 == 4, 0xaa, 0x00)
} else if val < 16 {
// r = val & 1 ? 0xff : 0x55;
r = compareVal(val&1 == 1, 0xff, 0x55)
g = compareVal(val&2 == 2, 0xff, 0x55)
b = compareVal(val&4 == 4, 0xff, 0x55)
} else if val < 232 { /* 6x6x6 colour cube. */
r = (val - 16) / 36 * 85 / 2
g = (val - 16) / 6 % 6 * 85 / 2
b = (val - 16) % 6 * 85 / 2
} else { /* Grayscale ramp. */
nv := uint8(int(val)*10 - 2312)
// set value
r, g, b = nv, nv, nv
}
return []uint8{r, g, b}
}